Boilers classically involve the flow of water between an upper steam drum and a lower water drum or header. Steam is removed from the upper steam drum and feed water is replaced therein to flow downwardly, as cooler water through a conduit conventionally known as a downcomer to the water drum or header. Water from the lower drum or header rises to the steam drum through risers which are conventional boiler tubes that are heated in the radiant or convection section of a boiler. Steam is generated in these riser tubes. The steam is separated from the water in the steam drum.
Boilers of this class are frequently very large, and of considerable height, such as ten to twelve stories high. They have very hot combustion chambers. Some have chemicals in the furnace. If water contacts the chemicals, steam will instantly be generated at great pressure, and can cause disastrous explosions. A classical source of such water is the rupture of one of the riser (boiler) tubes which releases water into the combustion chamber.
This anticipated risk is guarded against by rather elaborate systems for dumping water (rapid draining) from the system as quickly as possible after the detection of a leak. A conventional technique is to actuate a plurality of dump valves, each of a very large size. During the rapid drain of the boiler the operating personnel have no indication of the water level remaining in the boiler. Many people have been killed while trying to examine the furnace in which a tube was leaking water into the furnace. A furnace explosion occurred while they were peering into the furnace.
For example, suppose that the dump system relies for its indication upon the fact that the shaft of a dump valve has been turned as verification that the water has in fact been dumped. This does not preclude the condition that perhaps the valve shaft has sheared off, or that the outlet pipes are plugged or a block valve is inadvertently left closed. In these cases, the draining process will be slower, thus permitting more water to enter the combustion chamber. Thus in the absence of an absolute assurance that all of the water in the system has been dumped, a person should not expose himself to the risk of investigation. Instead, he should stay in the safety of the block-house control room until the situation has resolved itself. Unfortunately, this resolution can involve very serious damage to the boiler, which might have been avoided had there been proper knowledge of the actual condition of the water level in the boiler system.
It is an object of this invention to provide an elegantly simple, reliable, and in its best embodiment, a passive system for providing information regarding the status of the water level in the boiler over its entire height. The system operates under normal conditions and emergency conditions.